Electronic device



c. H. BROWN ELECTRONIC DEVICE,

Filed Sept. 28, 19:57

Nov. '28, 1939.-

T0 :3 UTILIZATION E CIRCUIT INVENTOR.

I/IZLES H. BROWN mrv-(A/ Y ATTORNEY.

Patented Nov. 28, 1939 UNITED STATES ELECTRONIC DEVICE Charles H. Brown, Brooklyn, N. Y., assignor to Radio Corporation of America, a. corporation of Delaware Application September 28, 1937, Serial No. 166,071

'7 Claims.

The present invention relates to electron discharge device circuits of thetype employing a cold cathode surface functioning by secondary emission of electrons for the production of elec- 6 tron multiplication. The broad principle of operation of devices of this type is described in United States Patent No. 2,121,067, granted June 21, 1938, to me and Walter Van B. Roberts, jointly.

More specifically, the present invention concerns a cold cathode electron discharge device wherein the production of electron multiplication and the collection of electrons are separated, and further wherein the electrons diverted lv from the electron multiplication portion of the system are still further multiplied in the same evacuated envelope. In one aspect, the invention provides a multi-st'age electron multiplier within a single envelope, one stage drawing its energy from an oscillating cloud of electrons in another stage.

One of the objects of the present invention is to provide a multi-stage electron multiplication amplifier within a single envelope, so that load conditions in the electron collector stage have little or no effect on the loading of the preceding multiplication stage.

Another object is to provide a multi-stage electron multiplication device having a combined electron collector and multiplier stage which is electron coupled to a multiplication stage, and which may be readily modulated.

These and other objects, features and their advantages are set forth in the following description, which is accompanied by a drawing wherein:

Figs. 1 and 2 illustrate, by way of example only, two multi-stage electron multiplier circuits embodying the principles of the invention.

The broad principle of operationof the cold cathode device, as set forth in my United States Patent No. 2,121,067, supra, requires the presence of an oscillating cloud of electrons between two cold cathodes which are designed to emit copious secondary electrons upon being bombarded by other electrons. These cold cathodes are preferably oppositely disposed with respect to a central accelerating anode in the form of a ring or wide mesh grid, the latter being maintained at a positive potential relative 'to the cathodes which, in turn, are coupled together by a resonant circuit. The electrons are prevented from immediately impacting the central accelerating electrode either by a coil surrounding the envelope for producing a magnetic fi eld perpendicular to the plane of the central electrode, or by the construction of the cathodes, as described and illustrated in my above mentioned patent. The operation of the device is usually initiated by casual electrons free to move in the envelope, produced by radioactivity, thermal agitation, photoelectric efiect, or otherwise. These casual electrons are accelerated toward and pass through the anode, impacting on one of the cold cathodes with a velocity sufficient to dislodge a number of secondary electrons. These secondary electrons, inturn, are drawn toward the opposite cathode where they arrive half a period later to dislodge a still greater number of secondary electrons which will repeat the process of the first electrons. This building up process will continue until there .is a dense cloud of electrons oscillating back and forth between the cathodes, and equilibrium is established when the average absorption of electrons by the anode is equal to the net loss of electrons by secondary emission from the two cathodes.

' The present invention utilizes a portion of the oscillating cloud of electrons in another structure and multiplies this portion before it is utilized.

With the foregoing general description in mind, let'us now turn to the drawing. Referring to Fig. 1, there is shown a tube having, within an evacuated envelope l, a pair of cold cathodes 2 and 3 oppositely disposed with respect to an intermediate ring-like or cylindrical anode 4 which is maintained by source 5 at a suitable positive potential relative to the cathodes. Cathodes 2 and 3 may be plates, as shown, or mesh affairs whose confronting faces are sensitized to emit'secondary electrons at a ratio greater than unity when impacted. Source 5 is connected to the midpoint of an inductance coil 6 which with a parallelly connected variable capacitance l forms a tuned circuit coupled between the two cathodes. Cathodes 2 and3 are excited in opposite phase by the tuned circuit 6, 1 whose res-- onant frequency is so related to the anode pctential that electrons traverse the space between the cathodes in atime corresponding to one-half a cycle; or putting it another way, whose resonant frequency is close to the full period of the oscillating cloud. An external electric field in the form of a coil 8 insures that the electrons make a definite number of traversals before being taken up by anode 4. Coil 8' surrounds the envelope l and is supplied with a direct current, as shown, for establishing a guiding magnetic i field for the electrons in the space between cathodes.

Cathode 3 is either a plate with an appreciably sized perforation in its center, or provided with a multiplicity of perforations, in the manner of a grid, through which flow intermittent pulses of electrons from the oscillating cloud toward a meshed collector disc 8 which is maintained by a battery H] at a high positive potential relative to the cathodes Z and 3. Due to the construction of the disc 8, the electrons drawn through cathode 5 will mostly pass right through the disc and impinge on electrode 9 which is treated to emit copious secondary electrons on impact. Electrode 9 is maintained at a lower positive potential than disc 8 by a battery II to insure that the electrons which pass through disc 8 do impinge on this electrode, instead of reversing their travel before striking. The potential on disc 8 insures that few or none of the secondaries emitted by electrode 9 reach the cathode 3. The time of electron travel between disc 8 and electrode 9 is designed to be small compared to the time of travel of the electrons between cathodes 2 and 3, and this is done by spacing the electrodes 8 and 9 closer together than the electrodes 2 and 3, and by suitable choice of applied potentials. It will thus be seen that each time the electron cloud between cathodes 2 and 3 reaches the plane of cathode 3, a certain number of electrons impact and create secondaries which are used to continue the multiplication process, but others of the electrons pass directly through the aperture in cathode 3 and create additional secondary electrons at electrode 9 before being collected by collector disc 8. We thus have in effect a twostage electron multiplier, the stage 8, 9 creating electron multiplication and being electron coupled, so to speak, to the stage 2, 4, 3.

The electrons collected by disc 8 cause a current to flow in resistor 12, in turn producing potential variations on the grid of a radio frequency amplifier l3 to whose output circuit is coupled any suitable utilization circuit.

An input circuit I5 is employed to impress on the tuned circuit 6, 1 radio frequency variations in accordance with the incoming signals. This input circuit may comprise an antenna, such as a dipole for applying signal variations to vary the voltage on the terminals of the tuned circuit connected to the cathodes, in order to influence the oscillating electron cloud.

Fig. 2 is a modification of Fig. 1 and shows a push-pull output circuit. For the sake of simplicity of the drawing no external electromagnetic guide coil has been shown, although it will be appreciated that such a coil may be dispensed with and an electric field for influencing the electrons obtained by the special construction of the cathodes. In this figure, both the secondary emissive cathodes 2' and 3' are perforated at O to permit electrons to be drawn from the oscillating cloud in the space between the cathodes, first through one cathode 2' and then through the other 3. The intermittent pulses of electrons passing through these cathodes flow first to the secondary emissive plates l6, l6 and then to collector grids I1, I! which are maintained at a positive potential relative to the cathodes 2. 3' and also relative to screen grids l8, l8 and plates l5, l6. These plates are treated to emit copious electrons when bombarded by the electrons drawn from the cathodes 2 and 3'. Screen grids l8, 18 are connected together, and are arranged in the form of slots to allow easy passage of electrons from the cathodes to the grids l1, l1. These screens are maintained at a positive potential relative to the cathodes but at a less potential relative to grids I1, I! and plates l6, IS. The potentials on grids ll, ll thus serve to prevent the secondary electrons emitted from anode plates l6, I6, caused by bombardment, from landing on the screen grids.

Output energy from the structure of Fig. 2 is obtained from coil 20, which is coupled to tuned circuit IS, in turn connected in push-pull to collector grids I1, I1.

Radio frequency input energy is inductively applied to tuned circuitB, 1 in the same manner as in Fig. 1, although it will be understood that if desired, capacitive coupling to the tuned circuit may instead be employed in both cases.

One of themany uses of the systems of Figs. 1 and 2 is an amplifier in a radio receiving system, or Where a parallel tuned output circuit is employed, as in Fig. 2, as a heterodyne detector or converter to produce a difference or beat frequency between the incoming signal frequency and the frequency of local oscillations produced by the oscillating cloud of electrons. To achieve the effect of a frequency converter in Fig. 1, a parallel tuned circuit should be placed between the grid and cathode of tube l3.

It is to be understood that the circuits illustrated are merely for the purpose of expounding the principles of the invention and that various modifications can be made without departing from the spirit and scope of the invention.

What is claimed is:

1. An electron multiplier comprising a pair of opposed surfaces capable of emitting secondary electrons which exceed in number the primary electrons impacting the same, at least one of said surfaces being apertured, means for causing an electron cloud to oscillate between said surfaces to create repeated multiplying impacts therewith, an electrode in a space outside the space between said surfaces for diverting through said apertured surface a portion of said cloud into said outside space, a surface located within said outside space and capable of emitting secondary electrons when impacted by said diverted portion, said electrode being located between said last surface and said pair of opposed surfaces.

2. An electron multiplier comprising a pair of opposed surfaces capable of emitting secondary electrons which exceed in number the primary electrons impacting the same, at least one of said surfaces being apertured, means for causing an electron cloud to oscillate between said surfaces to create repeated multiplying impacts there with, an electrode in a space outside the space between said surfaces for diverting through said apertured surface a portion of said cloud into said outside space, a surface located within said outside space and capable of emitting secondary electrons when impacted by said diverted portion, said electrode being located between said last surface and said pair of opposed surfaces, means for maintaining said outside surface at a positive potential and said electrode at a higher positive potential relative to said pair of opposed surfaces, the distance between said outside surface and said electrode being such and the potentials applied to the same being such that the time of electron travel between said electrode'and outside surface is less than the time of electron travel between said opposed surfaces.

3. An electron multiplier comprising a pair of opposed surfaces capable of emitting secondary electrons which exceed in number the primary electrons impacting the same, at least one of said surfaces being apertured, means for causing an electron cloud to oscillate between said surfaces 5 to create repeated multiplying impacts therewith, an electrode in a space outside the space between said surfaces for diverting through said apertured surface a portion of said cloud into said outside space, said electrode being apertured to allow passage therethrough of said diverted electrons, a surface located within said outside space and capable of emitting secondary electrons when impacted by said diverted portion, said electrode being located between said last surface and said 5 pair of opposed surfaces.

4. In combination, an electron discharge device comprising an evacuated envelope containing an anode and a pair of surfaces capable of emitting secondary electrons on impact by other 20 electrons, said pair of surfaces being oppositely disposed with respect to said anode, means for.

causing an electron cloud to oscillate between said surfaces, each of said surfaces being apertured to allow a portion of said cloud to pass 26 therethrough at the time of impact, a plate individual to each of said surfaces and located in a space apart from the space between said surfaces, said plates also being capable of emitting electrons on impact, a collector grid located be 30 tween each plate and its associated surface, means for maintaining said plates at positive potentials and said collector grids at higher positive potentials relative to said surfaces, whereby electrons passing through said apertures impinge on said 35 plates to produce electron multiplication, and a tuned power absorbing circuit connected to said grids.

5. In combination, an electron discharge device comprising an evacuated envelope contain- 40 ing an anode and a pair of surfaces capable of emitting secondary electrons on impact by other electrons, said pair of surfaces being oppositely disposed with respect to said anode, means for causing an electron cloud to oscillate between 45 said surfaces, each of said surfaces being apertured to allow a portion of said cloud to pass therethrough at the time of impact, a plate individual to each of said surfaces and located in a space apart from the space between said surfaces, said plates also being capable of emitting 5 electrons on impact, a collector grid located between each plate and its associated surface, means for maintaining said plates at positive potentials and'said collector grids at higher positive potentials relative to said surfaces, whereby elec- 10 trons passing through said apertures impinge on said plates to produce electron multiplification,

a screen grid located between each collector grid and its associated surface, means for maintaining said screen grids at positive potentials relative to said surfaces which are less than the positive potentials applied to said plates, and a parallel tuned power absorbing circuit connected to said collector grids. 1

6. In combination, a detector comprising a pair of opposed surfaces capable of emitting secondary electrons which exceed in number the primary electrons impacting the same, one of said surfacesbeing apertured, means including a resonant circuit for causing an electron cloud to oscillate between said surfaces to create repeated multiplying impacts therewith, an input circuit constituting a source of oscillations coupled to said resonant circuit, an electrode in a space outside'the space between said surfaces for diverting through said apertured-surface a portion of said cloud into said outside space, a surface capable of emitting secondary electrons when impacted by said diverted portion, said electrode being located between said last surface and said pair of opposed surfaces, and a load circuit coupled to said electrode and to said last surface adapted to be impacted by said diverted portion. 7. A system in accordance with claim 6, characterized in this that said tuned circuit coupled 4 to said electrode is tuned to the difference frequency between the frequency of said source of oscillations and the resonant frequency of said resonant circuit.

CHARLES H. BROWN. 

